The following story was originally published in our Manufacturing Outlook eZine. For a free subscription Click Here
by Royce Lowe
As some know, aluminum comes originally from bauxite, an ore that contains aluminum hydroxide, silica, and iron ore. The first step in aluminum production is the formation of alumina, or aluminum oxide, from bauxite. It takes 4 to 5 tons of bauxite to produce 2 tons of alumina, then 2 tons of alumina to produce a ton of aluminium. World reserves of bauxite are estimated at some 30 billion tons, so we’re not likely to run out soon. Guinea, Vietnam, Australia, and Brazil, in that order, account for some 21 billion tons of reserves.
Production of aluminum from alumina takes an awful lot of electricity, which is why the province of Québec was chosen in the seventies by companies from Canada and abroad to produce the metal. Québec’s electricity comes from hydro, from the James Bay project way up north in the province. Hence, the electricity is both cheaper and cleaner. But the process of taking the oxygen out of the alumina, and the gas’s combination with the carbon anode in the electrolysis process, leaves a serious carbon footprint.
Production of aluminum is based on the electrolytic reduction of alumina, which, as mentioned, is an energy intensive process (about 13-16 kWh per kg aluminum) and produces significant emissions of greenhouse gases, mainly direct process emissions from CO2 and PFCs, and indirect emissions from electricity production. The Hall-Heroult electrolytic process that was developed in the late 19th century still forms the cornerstone of the aluminum production process. Most of today’s aluminum production facilities use carbon anodes that are dipped into an iron vessel or ‘pot’ that functions as a cathode and contains cryolite (sodium aluminum fluoride) and alumina. The electrical energy that runs through the anode initiates and continues the smelting process, where the molten aluminum thus produced is tapped for casting and further processing. Some 3% of global electricity supply is consumed by the extraction of aluminum. And that’s for a mere 60 million tons. Just under 1% of total global greenhouse gas emissions come from the process.
Primary aluminum production consumes about 20 times more energy than recycled aluminum. Electricity consumption constitutes roughly one-third of the production costs, hence reducing electricity consumption is one of the industry’s R&D priorities. Aside from recycling, several technologies to improve the performance of the aluminum production process are available, such as the use of inert anodes, instead of the conventional carbon anode. Inert anode technology is seen as one of the more promising options for the industry for the years to come.
When carbon or consumable anodes are used, the reaction frees up the oxygen present in the alumina, but it immediately reacts with the carbon from the anode to form CO2. The process as such consumes over 400 kg of carbon anodes per ton of aluminum. Using inert (or non-consumable) anodes avoids the formation of CO2, so that only pure oxygen is produced as a by-product. If successfully developed and applied, inert anode technology could have significant energy, cost, productivity, and environmental benefits for the aluminum industry worldwide. When combined with other advances in electrolytic cell design, the technology should achieve even greater benefits.
Through all this, along came ELYSIS, a technology company that was created from a partnership between two global industry leaders – Alcoa and Rio Tinto. ELYSIS’ goal is to revolutionize the way aluminum is produced across the globe. The process eliminates all direct greenhouse gases from aluminum smelting, and instead produces oxygen. Alcoa, Rio Tinto, the Government of Canada, and the Government of Quebec provided a combined investment of C$228 million to create ELYSIS and to see this technology reach commercial maturity.
Carbon-free aluminium smelting came a step closer just over a year ago when ELYSIS successfully produced aluminum with no direct greenhouse emissions at its Industrial Research and Development Center in Saguenay, Québec. The production of aluminum at the ELYSIS Industrial Research and Development Center marked the achievement of a significant milestone, using a full industrial design at a size comparable to small smelting cells operating in the industry today. Work then focused on accelerating the scale-up of the ELYSIS technology towards the demonstration of even larger commercial-size cells in 2023.
Construction of these prototype cells is now well underway at the end of an existing potline at Rio Tinto’s Alma smelter. The smelting cells will operate on an electrical current of 450 kA, which is the commercial scale for many large, modern aluminium smelters. The industrial cells are designed to be used as a ‘drop-in’ replacement to retrofit existing smelters or build new ones, and can be scaled to size, as needed.
As things go, ELYSIS aims to have its technology available for installation from 2024, and the production of larger volumes of carbon-free aluminum approximately two years later.
This is an ambitious project, but it has two of the aluminum industry’s giants involved in it. It is being tested using hydroelectric power, which is not available everywhere. The carbon footprint would be quite a lot higher where electricity is generated from natural gas or (particularly) coal plants. We will watch with interest ELYSIS’ upcoming projects.
Author profile: Royce Lowe, Manufacturing Talk Radio, UK and EU International Correspondent, Contributing Writer, Manufacturing Outlook. ν